This invention relates to a device and method for in situ shortening of nuclear reactor zirconium alloy process tubes which have grown as a result of radiation exposure. More particularly, the invention concerns an in situ upsetting technique which involves inductively heating a short band of a process tube with simultaneous application of an axial load sufficient to cause upsetting with an attendant decrease in length of the process tube.
One particular reactor which has zirconium alloy process tubes which have grown as a result of radiation exposure is the N Reactor located at the Richland Operations Hanford Plant of The Department of Energy, Richland, Washington. N Reactor is primarily a large cube of stacked graphite bars penetrated horizontally by 1003 zirconium alloy process tubes and surrounded by a thick shield of very dense concrete to contain the radiation of the nuclear process. Uranium fuel assemblies are placed in the process tubes and high-pressure cooling water is pumped through these tubes to pick up the heat which is released from the uranium during the fission process. It has been discovered that the process tubes have been growing in length as the result of the radiation exposure. This tube elongation produces severe undesirable effects such as connector interference or packing gland-key interference.
Connector interference is caused by unequal growth rate of adjacent process tubes. Each process tube has a carbon steel inlet nozzle secured to its inlet (front) side. Attached to each inlet nozzle is a high-pressure inlet coolant connector pipe. Since there is an average 7/8 inch clearance between adjacent coolant pipes as the process tubes grow at unequal growth rates, the high-pressure coolant pipes are forced into contact with each other, thereby creating unwanted stress.
Packing gland-key interference is caused by the following. At the inlet end the process tube is attached to the inlet nozzle by means of a rolled joint. Surrounding the process tube and the attached portion of the inlet nozzle is a thimble. The end of the thimble is sealed against the inlet nozzle by a packing gland which is a dynamic gas seal designed to allow some movement of the process tube due to thermal expansion. Also four keys evenly space the inlet nozzle from the thimble and are provided for torsional rigidity. Since the tubes have grown unexpectedly as a result of radiation exposure, these keys come in contact with the packing gland. Further, since the thimble is rigidly secured to the reactor shield, the growth causes the shield to be pulled away from the reactor.
A possible method for correcting this unanticipated tube growth is to shorten the tube by an amount needed to correct the problem. The method must be safe, reasonably fast, and not compromise reactor integrity. It must also be capable of remedying either connector or packing gland-key interference.
It is therefore one object of the present invention to provide a device for in situ shortening a reactor process tube.
It is a further object of this invention to provide an in situ method for shortening a reactor process tube.
More particularly it is a further object of this invention to in situ shorten the process tube utilizing an upsetting technique which involves heating a short band of the process tube with simultaneous application of an axial load sufficient to cause upsetting with an attendant decrease in length of the process tube.
Finally it is an object of this invention to provide a device and method for shortening reactor process tubes which is safe, reasonably fast, and will not compromise reactor integrity.